Parkinson's disease (PD) is a neurodegenerative disorder characterized by selective degeneration and cell death of dopaminergic neurons in the substantial nigra region of the brain. Parkinson's disease was generally considered to be sporadic and of unknown etiology, but, in the last 15 years, there has been an important development of the understanding of the genetic basis of this disease and associated pathogenic mechanisms. One area of the development is the understanding of leucine rich repeat kinase 2 (LRRK2) protein. A number of mis-sense mutations in the LRRK2 gene have been strongly linked with autosomal dominant Parkinson's disease in familial studies (See WO2006068492 and WO2006045392; Trinh and Farrer 2013, Nature Reviews in Neurology 9: 445-454; Paisan-Ruiz et al., 2013, J. Parkinson's Disease 3: 85-103). The G2019S mutation in LRRK2 is the most frequent mis-sense mutation and is associated with a clinical phenotype that closely resembles sporadic Parkinson's disease. The LRRK2 G2019S mutation is also present in approximately 1.5% of sporadic Parkinson's disease cases (See Gilks et al., 2005, Lancet, 365: 415-416). In addition to the known pathogenic coding mutations in LRRK2, additional amino acid coding variants of LRRK2 have been identified that are also associated with risk of developing Parkinson's disease (See Ross et al., 2011 Lancet Neurology 10: 898-908). Furthermore, genome-wide association studies (GWAS) have identified LRRK2 as a Parkinson's disease susceptibility locus, which indicates that LRRK2 may be also relevant to sporadic Parkinson's disease cases without mutations that cause amino acid substitutions in the LRRK2 protein. (See Satake et al., 2009 Nature Genetics 41:1303-1307; Simon-Sanchez et al 2009 Nature Genetics 41:1308-1312)
LRRK2 is a member of the ROCO protein family and all members of this family share five conserved domains. The most common pathogenic mutation G2019S occurs in the highly conserved kinase domain of LRRK2. This mutation confers an increase in the LRRK2 kinase activity in in vitro enzyme assays of recombinant LRRK2 proteins (See Jaleel et al., 2007, Biochem J, 405: 307-317) and in LRRK2 proteins purified from G2019S PD patient-derived cells (See Dzamko et al., 2010 Biochem. J. 430: 405-413). A less frequent LRRK2 pathogenic mutation that confers amino acid substitution at a different residue, R1441, has also been shown to elevate LRRK2 kinase activity by decreasing the rate of GTP hydrolysis by the GTPase domain of LRRK2 (See Guo et al., 2007 Exp Cell Res. 313: 3658-3670; West et al., 2007 Hum. Mol Gen. 16: 223-232). Therefore, the evidence indicates that the kinase and GTPase activities of LRRK2 are important for pathogenesis, and that the LRRK2 kinase domain may regulate overall LRRK2 function (See Cookson, 2010 Nat. Rev. Neurosci. 11: 791-797).
There is evidence to show that the increased LRRK2 kinase activity is associated with neuronal toxicity in cell culture models (See Smith et al., 2006 Nature Neuroscience 9: 1231-1233) and kinase inhibitor compounds protect against LRRK2-mediated cell death (See Lee et al., 2010 Nat. Med. 16: 998-1000).
Induced pluripotent stem cells (iPSCs) derived from LRRK2 G2019S Parkinson's disease patients have been found to exhibit defects in neurite outgrowth and increased susceptibility to rotenone, that may be ameliorated by either genetic correction of the G2019S mutation or treatment of cells with small molecule inhibitors of LRRK2 kinase activity (See Reinhardt et al., 2013 Cell Stem Cell 12: 354-367). Increased mitochondrial damage associated with LRRK2 G2019S mutation in iSPCs is also blocked by genetic correction of the G2019S mutation (See Sanders et al., 2013 Neurobiol. Dis. 62: 381-386).
Additional evidence links LRRK2 function and dysfunction with autophagy-lysosomal pathways (See Manzoni and Lewis, 2013 Faseb J. 27:3234-3429). LRRK2 proteins confer defects in chaperone-mediated autophagy that negatively impact the ability of cells to degrade alpha-synuclein (Orenstein et al., 2013 Nature Neurosci. 16 394-406). In other cell models, selective LRRK2 inhibitors have been shown to stimulate macroautophagy (See Manzoni et al., 2013 BBA Mol. Cell Res. 1833: 2900-2910). These data suggest that small molecule inhibitors of LRRK2 kinase activity may have utility in the treatment of diseases characterized by defects in cellular proteostasis that result from aberrant autophagy/lysosomal degradation pathways including forms of Parkinson's disease associated with GBA mutations (See Swan and Saunders-Pullman 2013 Curr. Neurol. Neurosci Rep. 13: 368), other alpha-synucleinopathies, tauopathies, Alzheimer's disease (See Li et al., 2010 Neurodegen. Dis. 7: 265-271) and other neurodegenerative diseases (See Nixon 2013 Nat. Med. 19: 983-997) and Gaucher disease (See Westbroek et al., 2011 Trends. Mol. Med. 17: 485-493). Further, significantly elevated levels of LRRK2 mRNA have also been observed in fibroblasts of Niemann-Pick Type C (NPC) disease patients compared with fibroblasts of normal subjects, which indicates that aberrant LRRK2 function may play a role in lysosomal disorders (See Reddy et al., 2006 PLOS One 1 (1):e19 doi: 10.1371/journal.pone.0000019—supporting information Dataset 51). This observation suggests that LRRK2 inhibitors may have utility for treatment of NPC.
The PD-associated G2019S mutant form of LRRK2 has also been reported to enhance phosphorylation of tubulin-associated Tau (See Kawakami et al., 2012 PLoS ONE 7: e30834, doi 10.1371), and disease models have been proposed in which LRRK2 acts upstream of the pathogenic effects of Tau and alpha-synuclein (See Taymans & Cookson, 2010, BioEssays 32: 227-235). In support of this, LRRK2 expression has been associated with increased aggregation of insoluble Tau, and increased Tau phosphorylation, in a transgenic mouse model (See Bailey et al., 2013 Acta Neuropath. 126:809-827). Over-expression of the PD pathogenic mutant protein LRRK2 R1441G is reported to cause symptoms of Parkinson's disease and hyperphosphorylation of Tau in transgenic mouse models (See Li, Y. et al. 2009, Nature Neuroscience 12: 826-828). Therefore, these data suggest that LRRK2 inhibitors of kinase catalytic activity may be useful for the treatment of tauopathy diseases characterized by hyperphosphorylation of Tau such as argyrophilic grain disease, Pick's disease, corticobasal degeneration, progressive supranuclear palsy and inherited frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17) (See Goedert, M and Jakes, R (2005) Biochemica et Biophysica Acta 1739, 240-250). In addition, LRRK2 inhibitors may have utility in treatment of other diseases characterized by diminished dopamine levels such as withdrawal symptoms/relapse associated with drug addiction (See Rothman et al., 2008, Prog. Brain Res, 172: 385).
Other studies have also shown that overexpression of the G2019S mutant form of LRRK2 confers defects in subventricular zone (SVZ) neuroprogenitor cell proliferation and migration in transgenic mouse models (See Winner et al., 2011 Neurobiol. Dis. 41: 706-716) and reduces neurite length and branching cell culture models (See Dachsel et al., 2010 Parkinsonism & Related Disorders 16: 650-655). Moreover, it was reported that agents that promote SVZ neuroprogenitor cell proliferation and migration also improve neurological outcomes following ischemic injury in rodent models of stroke (See Zhang et al., 2010 J. Neurosci. Res. 88: 3275-3281). These findings suggest that compounds that inhibit aberrant activity of LRRK2 may have utility for the treatments designed to stimulate restoration of CNS functions following neuronal injury, such as ischemic stroke, traumatic brain injury, spinal cord injury.
Mutations in LRRK2 have also been identified that are clinically associated with the transition from mild cognitive impairment (MCI) to Alzheimer's disease (See WO2007149798). These data suggest that inhibitors of LRRK2 kinase activity may be useful for the treatment diseases such as Alzheimer's disease, other dementias and related neurodegenerative disorders.
Aberrant regulation of normal LRRK2 proteins is also observed in some disease tissues and models of disease. Normal mechanisms of translational control of LRRK2 by miR-205 are perturbed in some sporadic PD cases, where significant decreases in miR-205 levels in PD brain samples concur with elevated LRRK2 protein levels in those samples (See Cho et al., (2013) Hum. Mol. Gen. 22: 608-620). Therefore, LRRK2 inhibitors may be used in treatment of sporadic PD patients who have elevated levels of normal LRRK2 proteins.
In an experimental model of Parkinson's disease in marmosets, an elevation of LRRK2 mRNA is observed in a manner that correlates with the level of L-Dopa induced dyskinesia (See Hurley, M. J et al., 2007 Eur. J. Neurosci. 26: 171-177). This suggests that LRRK2 inhibitors may have a utility in amelioration of such dyskinesias.
Significantly elevated levels of LRRK2 mRNA have been reported in ALS patient muscle biopsy samples (See Shtilbans et al., 2011 Amyotrophic Lateral Sclerosis 12: 250-256) It is suggested that elevated levels of LRRK2 kinase activity may be a characteristic feature of ALS. Therefore, this observation indicated that LRRK2 inhibitor may have utility for treatment of ALS.
There is also evidence indicating that LRRK2 kinase activity may play a role in mediating microglial proinflammatory responses (See Moehle et al., 2012, J. Neuroscience 32:1602-1611). This observation suggests a possible utility of LRRK2 inhibitors for treatment of aberrant neuroinflammatory mechanisms that contribute a range of neurodegenerative diseases, including Parkinson's disease, Alzheimer's disease, multiple sclerosis, HIV-induced dementia, amyotrophic lateral sclerosis, ischemic stroke, traumatic brain injury and spinal cord injury. Some evidence also indicates that LRRK2 plays a role in regulating neuronal progenitor differentiation in vitro (See Milosevic, J. et al., 2009 Mol. Neurodegen. 4: 25). This evidence suggests that inhibitors of LRRK2 may have a utility in production of neuronal progenitor cells in vitro for consequent therapeutic application in cell based-treatment of CNS disorders.
It has been reported that Parkinson's disease patients bearing LRRK2 G2019S mutation display increased frequency of non-skin cancers, including renal, breast, lung, prostate cancers as well as acute myelogenous leukemia (AML). Since there is evidence to show that G2019S mutation in LRRK2 increases catalytic activity of the LRRK2 kinase domain, small molecule inhibitors of LRRK2 may have a utility in treatment of cancers, for example kidney cancer, breast cancer, lung cancer, prostate cancer (e.g. solid tumors) and blood cancer (See. AML; Saunders-Pullman et al., 2010, Movement Disorders, 25:2536-2541; Inzelberg et al., 2012 Neurology 78: 781-786). Amplification and over-expression of LRRK2 has also been reported in papillary renal and thyroid carcinomas, where co-operativity between LRRK2 and the MET oncogene may promote tumor cell growth and survival (See Looyenga et al., 2011 PNAS 108: 1439-1444.)
Some studies suggested that genetic association of common LRRK2 variants with susceptibility to ankylosing spondylitis (See Danoy P, et al., 2010. PLoS Genet.; 6(12):e1001195; and leprosy infection. (See Zhang F R, et al. 2009, N Engl J Med. 361:2609-18.) These findings suggest that inhibitors of LRRK2 may have a utility in the treatment of ankylosing spondylitis and leprosy infection.
Meta-analysis of three genome wide associated scans for Crohn's disease identified a number of loci associated with the disease, including the locus containing the LRRK2 gene (See Barrett et al., 2008, Nature Genetics, 40: 955-962). Evidence has also emerged that LRRK2 is an IFN-γ target gene that may be involved in signaling pathways relevant to Crohn's disease pathogenesis (See Gardet et al., 2010, J. Immunology, 185: 5577-5585). These findings suggest that inhibitors of LRRK2 may have utility in the treatment of Crohn's disease.
As an IFN-γ target gene, LRRK2 may also play a role in T cell mechanisms that underlie other diseases of the immune system such as multiple sclerosis and rheumatoid arthritis. Further potential utility of LRRK2 inhibitors comes from the reported finding that B lymphocytes constitute a major population of LRRK2 expressing cells (See Maekawa et al. 2010, BBRC 392: 431-435). This suggests that LRRK2 inhibitors may be effective in treatment of diseases of the immune system for which B cell depletion is, or may be, effective in diseases such as lymphomas, leukemias, multiple sclerosis (See Ray et al., 2011 J. Immunol. 230: 109), rheumatoid arthritis, systemic lupus erythematosus, autoimmune hemolytic anemia, pure red cell aplasia, idiopathic thrombocytopenic purpura (ITP), Evans syndrome, vasculitis, bullous skin disorders, type 1 diabetes mellitus, Sjogren's syndrome, Devic's disease and inflammatory myopathies (See Engel et al., 2011 Pharmacol. Rev. 63: 127-156; Homam et al., 2010 J. Clin. Neuromuscular Disease 12: 91-102).